Method and means for continuously annealing metal strips, wire and the like



Feb. 13, 1962 K. e. JONASON 3,021,128

METHOD AND MEANS FOR CONTINUOUSLY ANNEALING METAL STRIPS, WIRE AND THELIKE Filed Dec. 4, 1956 2 Sheets-Sheet 1 INVENTOR K'ARL GUNNAR JONAS ONFeb. 13, 1962 K. G. JONASON 3,021,128

METHOD AND MEANS FOR CONTINUOUSLY ANNEALING METAL STRIPS, WIRE AND THELIKE Filed Dec. 4, 1956 2 Sheets-Sheet 2 59 @111 ///l /////l 1111/! I r4g 1 [ll/rr/ rrr [III/I11 I l 1 Fig.3 MENTOR KARL GUNNAR JONASON BY v fATTORNEY The present invention relates to a method and means forcontinuously annealing metal strips, wire and the like by contact withone or more heat supplying rollers and while exchanging heat between thepart of the strip or wire entering said rollers and the part of thestrip or wire leaving said rollers.

The invention is particularly applicable to the treating of ferrousmetal and non-ferrous metals, for instance iron, steel, copper,aluminium etc.

Previously such material was commonly annealed in batches, in whichprocess coil of strips or wire rings of the material were introduced ina furnace and retained therein until attaining a desired temperature. Inconnection with an increased demand for a uniform quality and in orderto reduce t e production costs, however, one has been forced to providea continuous treatment. By this the disadvantage is avoided which ischaracteristic for the treatment of coils of strip in batches, viz. thesticking or welding together of the various coils of strip. In additionthereto a better quality is obtained for the finished prod uct due tothe fact that the heat treating will be more uniform. Different wayshave been suggested for carrying out the continuous annealing of strips.According to one 'of such suggestions the strip is carried through anelongated, horizontal furnace without being sustained during its passagethrough the furnace proper, guide rollers being disposed at both ends ofsaid furnace. By this the formation of scratches and other indentationsupon the strip have been avoided. Although this method may be preferredfrom many points of view it is not suited for annealing thick or verythin material, since in the first case it will be too stiff and heavy tobe handled in the described manner, whereas too thin a material will notprovide a sufficiently high production per furnace unit.

In parallel with this method it was suggested to use a vertical furnacewhich frequently is closed on top. In such an apparatus the strip isentered into and removed from the bottom of the furnace, a guide rollerbeing disposed in the furnace over which the strip is passed. Theheating of the strip takes place through convection and radiation,usually from electric radiators.

In this connection it was also suggested to heat the strip by supplyingheat directly from a heated guide roller, the strip being conveyed inclose engagement with said heated roller.

Experiences from this latter method have proved, however, that it isimpossible to overcome the problem which arises in view of theelongation of the strip due to thermal expansion. In such case the stripthus will slide over the heat supplying roller so that scratches in itcannot be avoided.

The primary object of the invention, including methods and apparatus, isto solve the problem that lies in the thermal expansion of the strip orwire material without subjecting the strip to damage. A further objectresides in increasing the efiiciency of the method embodying theinvention by effecting a regenerative return of heat, otherwise going towaste, to the process, as will hereinafter more fully appear.

tits l ar In accordance with the invention exchange of heat is effectedby means of heat transmitting rotating rollers which absorb heat byconduction from heated material reviously heated by heat from an outsidesource to effect the annealing or other heat treating step and transmitthe absorbed heat by conduction to material to be annealed or otherwiseheat treated prior to its being heated for that purpose by heat derivedfrom said outside source. I

The invention will be more fully explained in the following withreference to a diagrammatic embodiment of the same shown in theaccompanying drawing and in con nection therewith further characteristicfeatures of the invention will be set forth.

FIGURE 1 is a vertical elevation, partially in section, of a heatingfurnace constructed in accordance with the invention, showing thearrangement of the rollers involved in the invention with feeding meansfor the strip or wire material in relation to said furnace.

FEGURE 2 is a plan view of FIGURE 1.

FIGURE 3 is a section on line IIIIII of FIGURE 1 With reference toFlGURE 1 reference numeral 10 designates a vertical stationary frame orstand for supporting one or more heat supplying rollers 11 and aplurality of heat conductive rollers 12. As will be evident from thisfigure the heat supplying roller 11 has no central shaft of rotation,but is supported for rotation, in

this case, by two supporting rollers 13. The rollers 12, however, areconventionally mounted by means of gudgcons in preferably cooledjournals 14. As will also be evident from the figure all rollers aredisposed at a suitable distance apart, guide rollers designated by lSbeing provided in the space between adjacent rollers for a purpose whichwill be described later on.

The rollers may be housed in a compartment or chamber, designated by 16,which is constituted by two displaceable housing halves 17 and 18 havingthick walls, roof and bottom and for the major part including a suitableinsnlating material applied in furnaces. Both halves l7 and 18 areprovided, in theernbodirnent shown, with wheels 19 running on rails orthe like 253 and each may be moved to one side of the frame ill. Mountedin the insulation in the lower part of one 1'7 of the halves are anumber of guide rollers 21 andmounted in the corresponding part of theright half 18 are guide rollers 22. Furthermore outer guide rollers 23and 24, respectively, are mounted for rotation at the halves '17 and 18.The guide rollers 21 and 22 are suitably hollow and mutually connectedso as to form a circulating system, which may include a heating medium,e.g. water, which is positively circulated through said rollers. Locatedon the side of the half 17 are'two stationary frames or supports 25 and26 and located on the side of the half 18 are two similar frames orsupports 27 and 28 On the last-mentioned side is also a frame 29. Theframes 25 and 26 each support a reel 30 and 31, respectively. Likewisethe frames 27 and 28 carry each one reel 32 and 33, respee tively. Thereels 30 and 31 may be braked by means of an especial brake means, whichin the embodiment shown comprises brake shoes or the like (not shown)and are loaded by means of weights 34 and 35, respectively, hanging fromwires 36 and 37, respectively.

With reference to FIGURES 1 and the frame 29 supports an electricdriving motor 38, which via a gearing, generally designated by 39,operates a shaft 40, having arranged thereon on one hand a drivingroller 41 and on the other hand two driving wheels 42 and 43,respectively, both said last-mentioned wheels being 'of equal diameter.Pivotally mounted above are driving roller 41 are two guide rollers 44and 45. The driving wheel 43 is pivotaily connected, by means of achain,

strap or the like 46, with the shaft of the reel 32, and in a similarway the driving wheel 42 is connected, by way of a chain, strap or thelike 47, with the reel 33. On the side of the half housing 17 is a brakemeans generally designated by 48, which may be constituted of twocompressible felt bodies 49' and d, at least one of said felt bodiesbeing hydraulically, pneumatically or mechanically actuated upon.Instead of felt material obviously other soft materials may be employedwhich do not give rise to scratches in a strip passing between saidbodies. By means of the hydraulic or pneumatic frictional means 48 anadequate braking surface pressure may be adjusted as desired for apurpose which will be explained later on.

The arrangement according to the invention operates in the followingway:

Assuming that a coil of metal strip 51 adapted to be heat treated isplaced upon the reel 31, an entering part 52 is led from the coil 51over the guide roller 23 and between the felt bodies of the brake means4-3. Thereafter the leading end of the strip is entered through anentrance 53 in the half housing 17 and passed over the guide rollers 21onto the left guide roller 15. From here the said end of the strip bendsupwardly and is allowed to pass over the lowermost heat conductiveroller 12 through a certain arc of its periphery and then passesupwardly onto the next roller 12 against which the strip will be pressedby means of a further guide or pinch roller 15. In a similar way thestrip continues along the superposed heat conductive rollers 12, againstwhich it is pressed by the pinch rollers 15. After the leading end ofthe strip has left the topmost heat conductive roller 12 it is allowedto pass over the heat supplying roller 11, being arranged in aparticular way, against the periphery of which it is caused to restthrough a considerablearc, the entering part of the strip thus changingits direction of movement and actuated by further pinch rollers 15 beingcaused to pass in a close contact with the opposite side of the heatconductive rollers. The return part, after having passed the lowermostroller 12, is carried over a guide roller 15 and the guide rollers 22.out of the housing 17, 18 over the guide roller24. From this latterguide roller the said return part further travels via a guide roller 44over the driving roller 40 and after having travelled along itsperiphery over the guide roller 45 to be coiled on the reel 32. In orderto provide for a substantially continuous operation, in the embodimentshown, a double equipment of the reels is arranged on either side of thehousing so as to obtain an auxiliary reel 30 on the entering side and anauxiliary reel 33 on the outgoing or discharge side. Preferablyprovisions are made for the arrangement between the reels and thefurnace on either side thereof, of stored strip quantities or,principally considered, coils of the strip adapted to be treated beingadjustable to its length, so that the length of the strip in the coilsmaybe suited to the time that will be consumed for connecting togetherand separating respectively two successive strips in the process. Thus,it is possible to work alternately with both said reels while theannealing process is taking place in the furnace in order to gain timefor joining, in one way or the other, the ends of the strips ofdifferent coils in order to avoid the opening of the furnace again. Inthis connection it should be mentioned that, in order to avoid thetrouble residing in the necessity of carrying out the above loadingprocedure at each start after a stop in the annealing operation, alength of strip is entered into the furnace at such stops and allowed toremain in the furnace.

As an alternative the furnace may be provided with one or more endlesschains which will be passed along the path of travel of the strip,preferably at the ends of the rollers.

In accordance with FIGURE 3 the heat supplying roller 11 is provided ateach side with a flange 54 and 55, respectively, which, however, are notindispensable.

Furthermore it should be noted that the heat supplying roller 11 ishollow and provided with a plurality of surface extending members takingthe form of pins or points 56 of metal. Furthermore the roller hasentirely open ends 57 in front of which stationary burners 58 areplaced, to which will be supplied, from any suitable outer source, fuelgas mixtures, which 'are caused to burn inside said roller 11. Theresulting combustion gases escape into the furnace compartment 16through the openings 57 in the roller 11 and may form a protecting gasfor the strip in course of heating. In a preferred plant the gases maybe exhausted continuously, by means of a fan or the like, through one ofthe openings in the lower parts of the furnace walls. By this theprotective gas may be distributed in a suitable way throughout thefurnace compartment 16. Also other sources of heat than burners areobviously applicable within the scope of the invention but it has provedthat the most concentrated supply of heat is obtained by means of suchburners.

In view among other things of the difiiculties em countered inconstruction in connection with the mount ing of such a roller havingcentrally entered burners, in accordance with the invention theconventional mounting by means of gudgeons or by means of a shaft hasbeen abandoned and in lieu thereof the entire roller 11 sup ported forrotation upon supporting rollers 13, one of which is shown in asectional view in FIGURE 3. This supporting roller is formed at bothends with shoulders or flanges so that the roller 11 obtains a carefulguiding and support. It cannot be avoided that the roller 13 will besubject to certain stresses due to heat, which may affect their bearingsand for this purpose the supporting rollers in accordance with FIGURE 3are assumed. to be supported in especial cooled bearings, generallydesignated by 59 and 69, respectively.

After the plant has been operated up to running con dition as far as thedistribution of heat is concerned, the entering part, as previouslydescribed, continuously travels over the rollers 12 and finally over theupper heat supplying roller 11 in close contact with it while the stripis being subject to the annealing process. The return part then in aheated condition again passes over the heat conductive rollers 12 on theopposite side, however, and during this passage said rollers will absorba major part of the heat accumulated in the return part, which isthereby successively cooled down to a suitable final temperature uponleaving the lowermost heat conductive roller. However, at the same timethe entering part travels along the opposite sides of the rollers 12,this part then being preheated by the heat transferred by the rollers 12due to the mechanical heat transfer occurring by means of the rollerswhen they rotate from. the return side towards the entering side. It hasproved that this method offers a very promotive distribution of heat andpreheating of the entering part respectively, before it attains the heatsupplying roller 11, where the true annealing process is brought about;This distribution of heat new contributes to the removal of the previousdifficuities due to thermal expansion met with in such annealing plants.Due to the fact that the temperature'of the entering part issuccessively increased to a considerable amount, the diir'erence inlength, which is due to the thermal expansion, will be compensated forin an effective way so that the part of the strip, which passes over theheat supplying roller 11, will be in close contact with it, and not, asin previous plants, removed from its surface due to the thermalexpansion, which would result in an impaired heat treatment. By keepingthe difference in temperature between the part being passed to theroller 11 and the corresponding return part at a minimum, only a smallheat expansion is en countered and therewith a small slipping movementand also a reduction of the formation of scratches will be the result.

In order further to compensate possibly still remaining criticaldifierences due to changes in length of the strip the brake means 36,34, 37, 35 and the felt brake 48 have been arranged on the entrance sideof the strip 52, the felt brake pressing against the strip while brakingit. Obviously it is not necessary to employ both said brake means sinceonly one of them would sufiice, but both of them have been shown for thepurpose of illustration. However, both said devices may be preferredwhen joining successive strips. Said braking devices exert a restrainingpull or tension on the entering part of the strip, which tension will bepresent at all rollers in such a way that the strip will be brought intoa close contact with their peripheries, thereby obtaining an even heattransfer 'all over the surface.

As will be apparent from the foregoing the invention provides a processor cycle of operation that is highly eficient from a thermal standpointin that it effects regenerative heat exchange operative to recover heatpreviously imparted to the strip material, which would otherwise go towaste, as the treated strip material cools to normal temperature and toreturn the recovered heat to the strip material to preheat the sameprior to the final heating to desired temperature by the addition ofheat from an outside source requiring the combustion of fuel to produce.In effecting this regenerative heat exchange for the purpose ofpreheating the strip material by means of heat which would otherwise goto waste, the heat conductive rollers 12 provide a series of what may betermed heat transfer stations that are sucessively passed by the stripmaterial as it is fed to and removed from the heating roller whichsupplies heat to the material from an outside source and which latterroller may be said to provide a heat treating station. Further, each ofsaid heat transfer stations may be said to include a heat absorbingstation at which heat is absorbed by conduction from the heated strip bya heat conductive roller and a preheating station to which heat istransferred by conduction from the conductive roller to strip materialbeing fed to the heat treating station for final heating to desired heattreating temperature. It is further to be noted that the process alsoprovides what is in effect coun-tercurrent heating flow in theregenerative preheating of the strip, in that when a plurality of heatconductive rollers are employed such rollers are passed successively ininverse order by portions of the strip being fed to the heat treatingstation and being withdrawn therefrom. With such an arrangement thestrip is initially preheated by heat transfer at a relatively lowtemperature level, is further preheated at the succeeding heat transferstation at a higher temperature level, and so on until at the final heattransfer station heat transfer is effected at the highest temperaturelevel. This provides for the most efficient and economical recovering ofall of what would otherwise be waste heat.

In order to further improve the heat economy, as has been indicatedabove, a heat absorbing fluid may be caused to pass for instance throughconnecting lines 63 and 64 shown in FIGURE 2 between the guide rollers21 and 22 in a direction from the latter towards the former ones so thatthe strip will be subject to a certain heat supply while being entered.

The strip is driven by the motor 38 over the roller 41 and is thereafterpositively coiled either on the reel 32 or on the reel 33, which, asdescribed above, are driven from the driving shaft 40 over chains 46 and47.

In view of the differences in the speed of rotation of the reels 32 and33 with increasing diameter, which prevails while the strip is beingcoiled, frictional coupling members of a kind known per se generallydesignated by 61 and 62, respectively, are provided, which adjust thespeed of rotation of the reels according to said increase in diameter ofthe coil of strip being wound.

An important feature of the invention resides in the fact that therollers are mounted in a stationary frame or stand and that a chamber orcompartment around them 6 is formed by movable walls or half housings.This will permit, upon the first loading of the plant or at repair, theseparation of both halves so as to provide access to the variousrollersfor passing the leading end or the strip over them. Thereafterboth said halves may be pushed together forming the said chamber again.

With this plant a continuous operation can be carried out, the plantdischarging a uniformly heat-treated strip or wire material, which ischaracterized by a uniform quality. The invention thus solves theproblem encountered in producing an optimally scratchless product at thesame time as the operation may be substantially continuous andconsiderably more rapid than was the case hitherto. As will be apparentfrom the foregoing description, the invention .is equally applicable tovarious kinds of long lengths of materials such as wire, sheet metalstrips, and other forms of metallic material that may be produced inlong lengths and which require annealing.

It is consequently to be understood that in the ensuing claims, whichdefine the invention, the term strip or strip material is intended to begeneric to all such forms of material whether it be in the form of wire,sheet metal strip, grid material, or any equivalent thereof, since thespecific nature of the material treated In accordance with theprinciples of the invention is not critical thereto. Consequently, theterm strip or strip material is to be interpreted as broadly coveringany continuous length of material that may be treated in accordance withthe principles of the method and apparatus of the invention.

The invention is not limited to the embodiment shown and described butmay be varied in various respects within the scope of the basicinventive idea.

Having now described the invention, what- I claim as new and desire tosecure by Letters Patent, is:

1. In a heat treating process of the kind in which metallic strip iscontinuously fed to a heat treating station at which it is heated withheat derived from an outside source, that improvement which comprisesregeneratively preheating the strip by feeding the strip serially past aseries of heat transferring stations on its way to said heat treatingstation, feeding the strip serially past said heat transferring stationsin reverse order after it has left said heat treating station, absorbingheat by conduction from the heated strip at each of said heattransferring stations and transmitting by conduction at each of saidheat transferring stations the heat absorbed at that station to thestrip being fed to said heat treating station.

2. In a method for continuously heat treating metal strip by causing thestrip to traverse in heat absorbing contact a heat treating rollerderiving heat from an outside source, that improvement which consists incausing the strip to traverse an arc of the periphery of a heattransferring roller in heat exchanging contact with the surface thereofprior to traversing said heat treating roller to be heated thereby andcausing the strip after leaving said heat treating roller to traverse asecond and differently located arc of the periphery of the same heattransferring roller in heat transmitting contact with the surfacethereof, whereby said heat transferring roller absorbs heat byconduction fro-m heated strip that has left the heat source at said heattreating station to raise the temperature of the strip to desired heattreating temperature, re-

moving heat from the heated strip by conduction at successively lowertemperature levels at each of said plurality of heat transfer stationsas the strip passes said stations after leaving said heat treatingstation and transmitting the heat thus abstracted from the strip atsuccessively higher temperature levels by conduction to the strip as itpasses said heat transfer stations before reaching said heat treatingstation, whereby to progressively preheat the strip prior to the heattreatment thereof with heat recovered from the strip following its heattreatment. 10 2,

UNITED STATES PATENTS Morgan Dec. 18, 1917 Whitehead et a1 Sept. 28,1926 Schon Feb. 13, 1940 Webster May 21, 1940 Erby Dec. 17, 1940 ShepardJune 9, 1942 Lorig Mar. 4, 1952

